1. Field of the Invention
This invention relates to a heat accumulating apparatus for a vehicle such as an automobile, and a heat accumulating method thereof. More particularly, the invention relates to a hot coolant type heat accumulating apparatus for a hybrid vehicle, and a heat accumulating method thereof.
2. Description of the Related Art
One type of hot coolant type heat accumulating apparatus for a hybrid vehicle that has been known in the past is disclosed in Japanese Patent Laid-Open Publication No. 2001-65384, for example, which is currently being submitted for application by the applicant of this application. This hot coolant type heat accumulating apparatus recovers some of the engine coolant that has been heated by the engine after the engine has warmed up and stores it in a heat accumulation tank as hot coolant. Then during a cold start of the engine, the hot coolant type heat accumulating apparatus replaces some of the engine coolant with the hot coolant stored in the heat accumulation tank so as to warn the engine.
As a result, according to the hot coolant type heat accumulating device described above, it is possible to improve cold startability of the internal combustion engine as well as reduce exhaust emissions compared to when the hot coolant type heat accumulating apparatus is not provided.
Generally, recovery of the hot coolant by the hot coolant type heat accumulating apparatus is done by taking some of the heated engine coolant as hot coolant from the cooling system of the engine and supplying it to the heat accumulation tank, and then discharging an equal amount of coolant as the hot coolant from the heat accumulation tank and returning it to the cooling system of the engine. Further, the heated engine coolant is also used as a heat source for a heater for warming a passenger compartment when necessary, by having some of the heated engine coolant taken from the cooling system of the engine and circulated through the heater.
The coolant in the cooling system of the engine is circulated by a coolant circulation pump that is driven by operation of a rotating shaft of the engine. The hot coolant recovery and the supply of circulated heated coolant to the heater also use the circulating action of the coolant by the coolant circulation pump. Therefore, in a vehicle in which the internal combustion engine has been automatically shutoff in response to the running state of the vehicle, circulation of the heated coolant for the heater is performed by coolant circulating means for when the engine is shutoff, such as an electric pump.
Therefore, when the internal combustion engine is automatically shutoff during hot coolant recovery and the coolant circulating means for when the engine is shutoff is operated, hot coolant flows out from the heat accumulation tank from the circulating action of the coolant by the coolant circulating means for when the engine is shutoff. As a result, the temperature of the hot coolant within the heat accumulation tank drops, which may prevent an effective improvement in cold startability of the internal combustion engine as well as an effective reduction in exhaust emissions.